nhdoc, I'd attribute it to a case of Dumb and Dumber. Being a professional tech doesn't mean that you're good at what you do, just that you get paid for it. Many techs have poor/no diagnostic ability. All they do is replace parts. The Service Department charged MBUSA for the work they did on your car even though it didn't fix the problem. Why the Service Advisor would think that the aftermarket glass was causing the problem is a good question. As far as MBUSA knows the regulator needed replacing and you're a satisfied customer. In fact, the Service Department did unnecessary work that was backcharged to MBUSA. Perhaps your dealer's Service Department is slow and makes money doing phantom work. The Service Advisor at our local dealer informed me months ago that their service business was very slow, and that most of their work was warranty-related. Things have picked up since then.

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Fred Hoelzle